Field application of polymer-based electrical insulation

ABSTRACT

Methods are disclosed for producing an insulated electrical conductor. Electrically uninsulated portions of respective electrical conductors are connected. A joint between the electrically uninsulated portions is coated with a preceramic resin, which is heated to cure the preceramic resin into a green-state insulator that substantially covers the joint.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 11/351,654, entitled “IN SITU PROCESSING OF HIGH-TEMPERATURE ELECTRICAL INSULATION,” filed Feb. 9, 2006 by Matthew W. Hooker et al., the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

This application relates generally to high-temperature electrical insulation. More specifically, this application relates to in situ processing of high-temperature electrical insulation. Certain examples described in detail relate to oil-recovery applications.

In recent years, concerns regarding the availability of sufficient oil to meet demands have been increasing. This is due in part to the fact that global demand for petroleum has been increasing and continues to increase, particularly as developing nations evolve more mature petroleum-consumption patterns that parallel those of developed nations. No near-term curtailment of this pattern of increasing demand is foreseen, and it is estimated that the oil industry will need to add on the order of 100,000,000 barrels/day in production to meet the projected rate of consumption by 2015. This pattern may be problematic by itself. But coupled with these increases in demand is also a growing recognition that oil recovery itself is likely to become more difficult over time. Very few new oil-field discoveries have been made since the 1970's, contributing to a general view that such discoveries are likely to be ever more infrequent.

The combination of increasing demand and increasing difficulty in production has resulted in a wide acknowledgment that there will be a production shortfall sooner than had previously been anticipated. There is accordingly an acute need in the art for improved methods for oil recovery. Associated with this increase in demand and production difficulties is an increase in the cost of oil which provides impetus and capital for the development of new sources of oil and the associated new production and recovery technology.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention provide methods for assisting oil-recovery processes that have thermal aspects. This may be done with a heater cable having a structure that is modified after installation. In particular, the heater cable includes a preceramic resin based composite that is pyrolyzed after deployment to form a ceramic insulator. While the ceramic insulator has material properties that are effective during use of the heater cable, fabrication, transportation, and installation of the heater cable may be simplified significantly when the preceramic resin, which is cured into its green state, is present instead of the ceramic insulator.

A first set of embodiments of the invention is accordingly directed to methods of producing a heater cable. An electrical conductor is coated with a preceramic resin. At least a portion of the coated electrical conductor is deployed into an operational location. The green-state preceramic resin is pyrolyzed while the at least a portion of the electrical conductor is in the operational location to convert the preceramic resin into a ceramic insulator disposed to electrically insulate the electrical conductor.

The coated electrical conductor may sometimes be sheathed within a sheath, with the at least a portion of the coated electrical conductor being deployed into the operational location by deploying at least a portion of the sheathed electrical conductor into the operational location. The ceramic insulator then electrically insulates the electrical conductor from the sheath. In one such embodiment, the preceramic resin is pyrolyzed by applying a direct-current voltage to the electrical conductor. In one embodiment, the coated electrical conductor is sheathed by welding the sheath to the coated electrical conductor. The coated electrical conductor may have a length between 1 and 5000 meters, in some instances being continuous without a splice or joint.

In other instances, the electrical conductor comprises a plurality of electrical conductors that are coated with the preceramic resin, with the at least a portion of the coated electrical conductor being deployed into the operational location by deploying each of the plurality of coated electrical conductors into the operational location. The plurality of electrical conductors are then electrically insulated from each other with the preceramic resin as well as after pyrolyzing the preceramic resin. In one such embodiment, the preceramic resin is pyrolyzed by applying an alternating-current voltage to the plurality of electrical conductors. In different embodiments, each of the plurality of coated electrical conductors may be sheathed with a sheath or the plurality of electrical conductors may collectively be sheathed with a sheath.

A variety of different specific compositions may be used in different embodiments. For example, the electrical conductor may comprise a solid copper rod. Examples of preceramic resins that may be used include inorganic preceramic polymers.

There are also a variety of ways in which the electrical conductor may be coated with the preceramic resin. In one embodiment, material pre-impregnated with the preceramic resin is wound around the electrical conductor. Material may be impregnated with a vacuum-pressure-impregnation or vacuum-assisted resin-transfer-molding process.

The preceramic resin may be cured into a green state before deploying the at least a portion of the sheathed rod into the operational location by heating the preceramic resin to a temperature between 15 and 250° C. In one embodiment, the temperature is between 125 and 200° C. The preceramic resin may be pyrolyzed by heating the preceramic resin to a temperature between 400 and 1500° C. In one embodiment, the temperature is between 750 and 1000° C. In some instances, the preceramic resin is pyrolyzed with a ramp-and-soak process: a temperature of the preceramic resin is increased monotonically for a first period of time and, thereafter, the temperature of the preceramic resin is maintained at an elevated temperature for a second period of time.

In a second set of embodiments, methods are provided for assisting an oil-recovery process. A heater cable is deployed into an oil-recovery environment. The heater cable comprises an electrical conductor coated with a preceramic resin. The preceramic resin is pyrolyzed while the heater cable is deployed in the oil-recovery environment to form a ceramic insulator by converting the preceramic resin, with the ceramic insulator electrically insulating the electrical conductor. In some embodiments, a temperature of the heater cable is increased to greater than 500° C. after pyrolyzing the preceramic resin to assist the oil-recovery process.

In some such embodiments, the heater cable further comprises a sheath within which the coated electrical conductor is disposed. The ceramic insulator electrically insulates the electrical conductor from the sheath. In such embodiments, the preceramic resin may be pyrolyzed by applying a direct-current voltage to the electrical conductor. In other embodiments, the electrical conductor comprises a plurality of electrical conductors coated with the preceramic resin. In some of those embodiments, the preceramic resin may be pyrolyzed by applying an alternating-current voltage to the plurality of electrical conductors. In those embodiments, the heater cable may comprise a sheath within which the plurality of coated electrical conductors are disposed

These embodiments find utility in different oil-recovery processes. For instance, in one embodiment, the oil-recovery process comprises a shale oil-recovery process. The heater cable is accordingly deployed into a shale deposit. Increasing the temperature of the heater cable causes kerogen present in the shale deposit to be converted to oil and/or gas. The oil and/or gas is accordingly available to be recovered from the shale deposit. In another embodiment, the oil-recovery process comprises a tertiary oil-recovery process or enhanced oil-recovery process. In such an embodiment, the heater cable is deployed into an oil field. Increasing the temperature of the heater cable causes a viscosity of the oil present in the oil field to be reduced. This oil may then be recovered from the oil field. In yet another embodiment, the oil-recovery process comprises an oil-sands oil-recovery process in which the heater cable is deployed on or near a ground surface of an oil-sands environment.

In various of these embodiments, the electrical conductor may comprise a solid copper rod and/or the preceramic resin may comprise an inorganic preceramic polymer. The preceramic resin may be pyrolyzed in the various manners described above. While the above summary has noted certain oil-recovery applications, these are intended only for purposes of illustration since the scope of the invention contemplates other applications also.

In still another set of embodiments, methods are provided of producing an insulated electrical conductor. A first electrically uninsulated portion of a first electrical conductor is connected with a second electrically uninsulated portion of a second electrical conductor. A joint between the first and second electrically uninsulated portions is coated with a preceramic resin. The preceramic resin is heated to cure the preceramic resin into a green-state insulator that substantially covers the joint.

In some of these embodiments, a compressive force may be applied to the preceramic resin while curing the preceramic resin into the green-state insulator to consolidate the preceramic resin. The compressive force may be applied by disposing a sleeve around the preceramic resin. The sleeve is made of a material having a volumetric thermal-expansion coefficient between about 10⁻⁴ and 10⁻² K⁻¹ and a Young's modulus between about 10⁵ and 10⁸ N/m². One example of such a material comprises silicone rubber. Alternatively, the compressive force may be applied by applying pressure to the preceramic resin with a pressurized containment system. In some instances, applying the compressive force comprises applying a resin containment film to the preceramic resin and disposing a sleeve around the resin containment film, with the sleeve and resin containment film subsequently being removed.

In certain instances, each of the first and second electrical conductors comprises an electrically insulated portion. Examples of electrical conductors that may be used in different embodiments include both solid electrically conductive rods and stranded electrical conductors.

Different methods may be used to cure the preceramic resin. For example, in one embodiment, the preceramic resin is cured by passing an electrical current through the first and second electrical conductors. In another embodiment, the preceramic resin is cured in a field location with locally mounted heaters. Both methods can be conducted in the field or in a manufacturing facility.

The methods of this set of embodiments may be incorporated into methods of assisting an oil recovery process. For example, the first conductor may be deployed into an oil-recovery environment, with curing of the preceramic resin converting the preceramic resin into a ceramic insulator that substantially covers the joint to form a continuous conductor. A portion of the continuous conductor corresponding to the second electrical conductor may then also be deployed into the oil-recovery environment. The process may be repeated with a third conductor to increase the overall length of the continuous conductor. Once the full length of the insulated conductor is assembled and the preceramic resin is cured to the green state, all the green-state insulation covering the first, second, and third conductors, as well as the regions where the first, second, and third conductors are joined can be pyrolyzed into a ceramic insulation in situ.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components.

FIG. 1 provides a schematic illustration of an in situ retorting process for recovering oil;

FIGS. 2A-2C are cross-sectional views of heater cables used in various embodiments of the invention;

FIGS. 3A and 3B are flow diagrams summarizing certain methods for field application of polymer-based electrical insulation in accordance with embodiments of the invention;

FIG. 4A is a flow diagram summarizing methods for oil recovery that may be performed in accordance with embodiments of the invention;

FIG. 4B is a graph illustrating a temperature profile that may be used for pyrolysis of an insulator in the heater cable of FIG. 2 according to some embodiments of the invention;

FIG. 5 is a flow diagram summarizing methods of using in situ pyrolysis of heater-cable insulation in a shale oil-recovery process;

FIG. 6 is a flow diagram summarizing methods of using in situ pyrolysis of heater-cable insulation in a thermal tertiary oil-recovery process;

FIG. 7 is a flow diagram summarizing methods for oil recovery that use field application of polymer-based electrical insulation on conductor joints; and

FIGS. 8A-8D are schematic illustrations of stages in executing the methods of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are directed generally at in situ processing of high-temperature electrical insulation. While much of the discussion that follows illustrates such processing with deployment of heater cables in certain oil-recovery environments, such illustrations are intended to be exemplary rather than limiting. As is noted below, embodiments of the invention find utility in a wide range of applications outside of oil-recovery techniques.

Those embodiments where the in situ processing is used to aid oil-recovery processes generally make use of certain thermal processes. In particular, these thermal processes rely on the deployment of heater cables that provide the thermal energy used in oil recovery. Such heater cables have a structure in which an electrical conductor is sheathed, with an electrical insulator being disposed to insulate the conductor from the sheath. Embodiments of the invention permit the heater cables to be deployed with a precursor to the electrical insulation in a green-state that is physically flexible but still electrically insulating. After deployment, pyrolysis of the green-state insulation forms a ceramic insulator that functions actively during the oil-recovery processes. The ability to deploy the heater cables with the flexible precursor permits the cable to be bent through curves and otherwise manipulated during deployment to a much higher degree than would be possible with the more brittle ceramic insulator. Not only does this make the thermal oil-recovery processes more efficient by reducing the risk of damage to the heater cables, it increases the variety of different environments in which deployment is possible.

1. Oil Recovery

There are a variety of different kinds of techniques used for oil recovery, with the specific nature of individual techniques often depending on geophysical properties of the region being explored. Techniques used in the development of oil fields are often categorized into three distinct phases of oil recovery: primary, secondary, and tertiary; tertiary recovery is also sometimes referred to in the art as “enhanced recovery.” As used herein, the term “oil field” refers to a terrestrial reservoir having a shape that traps hydrocarbons and that is covered by sealing rock.

Primary recovery uses the natural pressure of a reservoir as the driving force to push oil to the surface through a wellbore. During this recovery phase, wells may be stimulated through the injection of fluids, which fracture hydrocarbon-bearing formations to improve the flow from the reservoir to the wellhead. Pumping and gas lift may also sometimes be used during this phase to help production when the reservoir pressure dissipates. Currently, such primary-phase methods recover only about 10-30% of a reservoir's original oil.

Secondary recovery uses other mechanisms to produce residual oil remaining after the primary recovery. Examples of these secondary-recovery mechanisms include injection of natural gas to maintain reservoir pressure and water flooding to displace oil and drive it to a production wellbore. These techniques were developed shortly after World War II to extend the productive period of U.S. oil fields, and permit an additional 20-40% of the original oil reserve to be recovered. While these types of methods have successfully increased the quantity of oil that may be recovered from a field, still less than half the oil in place is typically recovered.

This has led to the more recent development of several tertiary oil-recovery techniques that offer prospects of ultimately producing 30-90% (or perhaps even more) of a reservoir's original oil. There are at least three major categories of tertiary recovery that have been found to be commercially successful to varying degrees. Techniques are employed to increase the mobility of the oil, which comprises reducing the oil's resistance to flow, and increasing the efficiency of the fluid or gas pushing the oil. Gas injection uses gases that expand in a reservoir to push oil towards a wellbore. Gases that have such properties include steam, natural gas, nitrogen, and carbon dioxide. In some other gas-injection forms of tertiary recovery, gases that dissolve in the oil and lower its viscosity have been investigated. Chemical injection uses surfactants to reduce the surface tension of the oil to enable it to travel through a reservoir to the wellbore. Thermal recovery uses a temperature increase to lower the viscosity of the oil and thereby improve its ability to flow through the reservoir. In some instances, this temperature increase is affected by introducing steam into the well. Thermal techniques account for more than 50% of U.S. tertiary recovery production, with gas injection making up the bulk of the remainder; chemical techniques currently account for less than 1% of tertiary recovery techniques in the United States.

Thermal techniques are also used in the recovery of oil from shale. Such a process extracts oil from the shale with the use of underground heaters to separate kerogen, the organic material from which oil is derived, from the shale in situ. This process is illustrated schematically with FIG. 1, which shows a shale deposit 104. As used herein, “shale” refers to detrital sedimentary rock formed by consolidation of clay into thin layers. Oil shale is found on all of the inhabited continents of the Earth, but many deposits are thin and irregular, yielding little oil. Unusually thick oil shale deposits are found in the western United States, providing roughly 75% of the world's estimated supply of recoverable oil shale resources. Although the exploration costs for oil shale are relatively low when compared with exploration for conventional crude oil, the recovery costs are notably higher. Kerogen does not flow as conventional crude oil does, and crushing does not free it from the host rock. Heat is accordingly used to remove kerogen from rock.

There are two principal methods that may use heat to extract oil from oil shale. In one method, known in the art as “retorting,” the oil shale is mined and the kerogen-containing rocks are heated to elevated temperatures. This process is economically inefficient because of the high cost of mining the oil shale and its relatively low yield. In one long-term project from 1980-1991, this technique extracted only 34 gallons of oil per ton of rock. Embodiments of the invention are instead directed to “in situ retorting,” in which holes are bored into underground shale deposits and heaters placed into the holes. The holes may be up to about 2500 feet deep in some embodiments, although the invention is not restricted to any particular hole depth. This process is illustrated in FIG. 1, with the heaters being identified with reference numbers 108. Activation of the heaters 108 produces heat 112 in the shale, raising its temperature sufficiently to convert the kerogen to oil in place. As used herein in discussions of kerogen conversion, “oil” refers to the conversion products. This process eliminates the shale mining costs and permits the newly formed oil to be pumped to the surface through a producer well 116. Temperatures greater than about 500° C. are sufficient to convert the kerogen into oil, and some heavier compounds may also be partially converted in lighter end products such as light oil and methane. The process is not only more cost effective than conventional retorting, but is also more environmentally benign because it eliminates the need to dispose of the mined shale once the oil has been extracted.

It is noted that the general structure of FIG. 1 also illustrates processes used for thermal tertiary oil recovery, with the deployed heaters 108 acting as a source of thermal energy 112 to lower oil viscosity and improve flow. In such instances, the heated oil may also be pumped to the surface through a producer well 116.

2. Heater Cables

Embodiments of the invention broadly encompass aspects related to the use of heater cables in thermal oil recovery techniques. The inventors have recognized that a process similar to that used for shale oil recovery may also be applied to other oil recovery processes, examples of which include tertiary recovery and recovery of oil from oil sands. In such embodiments, the heat used to lower the viscosity of the oil is supplied by heater cables deployed in an oil reservoir and heated to a temperature greater than 500° C. Heater cables like those described below may accordingly be used in a variety of different thermal oil-recovery techniques, of which tertiary recovery and shale recovery are used as examples for specific illustrations below.

One challenge presented by the use of electrical heaters for oil-recovery applications is the need to develop heater cables suitable for long-term high-temperature operation in downhole environments. To accommodate the geometry of the recovery environments, such heater cables are typically of long length, and may be of long lengths without splices or joints. For instance, in certain embodiments, the cable lengths may range from less than 1 meter to more than 5000 meters; in other embodiments, the cable lengths may be between 100 and 1500 meters. To function effectively in such applications, the heater cables need to provide sufficiently high power, preferably at high voltages, to maintain the desired temperatures. As noted above, it is when cables are heated to these temperatures that heat transferred to oil sufficiently lowers its viscosity that its flow characteristics permit it to be extracted during tertiary recovery processes. It is also at these temperatures that sufficient heat is transferred to kerogen to permit its conversion to oil in shale recovery processes. In some embodiments, it is preferable for the heater cables to have a similar durability while providing even higher temperature increases to the downhole environments. The additional heat transferred to oil at these higher temperatures in such applications as thermal tertiary recovery processes may result in even greater viscosity reductions to provide even better flow characteristics for the oil. One method to attain these higher heater temperatures applies higher voltages to the conductor, further electrically stressing the insulation. Voltages can range from 100 volts or less to 5000 volts or more, with both direct current and alternating current. Similarly, the conversion of kerogen to oil in shale recovery processes may be more efficient when the heater cables operate at higher temperatures and higher voltages. In some embodiments, the temperatures maintained by the heater cables exceed 700° C. and in still other embodiments, the temperatures maintained by the heater cables exceed 900° C.

Structures for heater cables used in embodiments of the invention are shown with the cross-sectional views of FIGS. 2A-2C. FIG. 2A illustrates a structure suitable for embodiments where direct current is to be used, while FIGS. 2B and 2C illustrate structures suitable for embodiments where alternating current is used. In the embodiment of FIG. 2A where direct current is to be used, each cable 200 comprises a central electrical conductor 204, surrounded by an electrical insulator 208, with the structure being embodied within a sheath 212. Merely by way of example, the central electrical conductor 204 may comprise copper or some other metal or metallic alloy and the sheath 212 may comprise a metal such as stainless steel. The insulator 208 electrically isolates the central conductor 204 from the sheath 212. The cables 200 typically have a length of 1-5000 meters, and may or may not contain joints or splices over this length, but the invention is not limited to any specific cable length. The outside diameter of the sheath 212 may be on the order of 1-10 cm in some embodiments, although the invention is not limited to any particular sheath diameter.

In the embodiments of FIGS. 2B and 2C where alternating current is to be used, each cable 240 or 240′ comprises a plurality of electrical conductors 220 surrounded by electrical insulation 224 that electrically isolates each conductor 220 from each other as well as from the surroundings. A sheath 232 or 232′ may be applied to the exterior of such a multiconductor structure to protect the cable 240 or 240′ during installation. In some instances, additional interior sheaths 228 may be provided for robustness and protection—for purposes of illustration, such interior sheaths 228 are shown in FIG. 2B, but could be omitted in the configuration of FIG. 2B or additionally included in the configuration of FIG. 2C. Similar to the direct-current configurations, the electrical conductors 204 may comprise copper or some other metal or metallic alloy, and the sheaths 228, 240, and 240′ may comprise a metal such as stainless steel. The cables 240 and 240′ again typically have a length of 1-5000 meters, and may or may not contain joints or splices over this length. The outside diameter of the multiconductor heater cables 240 or 240′ may be on the order of 1-20 cm, but the invention is not limited to any specific cable length nor to any particular cable diameter.

In certain embodiments, the insulator 208 comprises a ceramic material formed as a result of pyrolysis of a preceramic polymeric resin. Examples of suitable preceramic resins include polymer resins like those described in detail in commonly assigned U.S. Pat. No. 6,407,339, entitled “CERAMIC ELECTRICAL INSULATION FOR ELECTRICAL COILS, TRANSFORMERS, AND MAGNETS,” filed Sep. 3, 1999 by John A. Rice et al. (“the '339 patent”), the entire disclosure of which is incorporated herein by reference for all purposes. The '339 patent claims the benefit of the filing date of U.S. Prov. Pat. Appl. No. 60/099,130, filed Sep. 4, 1998, the entire disclosure of which is also incorporated herein by reference for all purposes. Preceramic polymers that may be used as precursors for the insulator 208 include monomers or polymers that are liquid at an application temperature and that will polymerize to form a solid compound, and which can be pyrolyzed at elevated temperatures to form a ceramic material. The polymer structure comprises inorganic molecules that link together to form chains. The ceramic material resulting after pyrolysis may comprise silica, silicon oxynitride, silicon carbide, silicon oxycarbide, a metal silicate, a metal nitride, a metal carbide, a metal oxycarbide, an alumina silicate, or other ceramic phases or mixtures thereof. While many preceramic polymers are based on silicon, the invention is not limited to such preceramic polymers and preceramics based on or containing other materials such alumina, magnesia, or zirconia are also within the scope of the invention. Other examples of preceramic polymers that may be used include polyureasilazane, hydridosiloxane, polysiloxane, polycarbosilazane, polysilazane, perhydropolysilazane, other organosilazane polymers, cyclosiloxane monomer, silicate esters, and blends thereof.

As noted in the '339 patent, different types of fillers or reinforcements may be used to modify the mechanical and/or electrical properties of the insulator 208, such as by addition of glass or ceramic powders to improve the compression strength and modulus of the insulator 208. A variety of glass or ceramic whiskers or fibers may be added to improve the shear and tensile strength of the insulator 208. In one embodiment, fibers having a composition of about 70% aluminum oxide, 28% silicone dioxide, and 2% boron oxide are used for fiber reinforcement.

3. Insulation Application

The deployment of heater cables described in detail below is an example of a more general process by which insulation may be applied to conductors in accordance with embodiments of the invention. Aspects of these general methods are summarized with the flow diagrams of FIGS. 3A and 3B. The application of insulation illustrated in FIG. 3A begins at block 304 by coating an electrical conductor with preceramic resin. The electrical conductor may take a number of different forms in specific embodiments. Merely by way of example, the electrical conductor may comprise an electrically conductive rod in the form of a solid or stranded electric conductor, may comprise mineral insulated cable, or the like.

The coating may be performed in a number of different ways. In one embodiment, a prepreg that includes the resin is wound around the electrical conductor. As used herein, a “prepreg” refers to material preimpregnated with resin; the material may be in the form of a mat, fabric, nonwoven material, roving, or the like. Merely by way of example, a vacuum-pressure impregnation (“VPI”) process or a vacuum-assisted resin-transfer-molding (“VARTM”) process may be used to impregnate material with the resin for winding around the electrical conductor. As will be known to those of skill in the art, VPI processes impregnate material under vacuum and pressure. In a further embodiment, the electrical conductor may be wrapped with a dry material and passed through a resin bath. Still other application methods may be used in different embodiments, including braiding and the like. In some instances, the entirety of the electrical conductor is coated with the preceramic resin, in which case the ceramic formed after curing may insulate the entirety of the electrical conductor. In other instances, a portion of the electrical conductor is coated with the preceramic resin so that other portions of the electrical conductor remain uninsulated after curing the preceramic resin.

The preceramic resin may be provided as a liquid, semiliquid, putty, paste, b-staged condition, or the like in different embodiments. In some instances, the preceramic resin includes inorganic binders, which may be particulate-reinforced or may contain nanoparticulate reinforcement. In other instances, no reinforcement is provided in the preceramic resin, in which case it is sometimes referred to as “neat resin.” As indicated at block 308, resin containment and release film may sometimes be applied over the preceramic resin in some embodiments.

At block 312, the resin is subjected to a compressive force that acts to consolidate the resin. In some embodiments, the compressive force is provided by installing a sleeve over the conductor/resin assembly, the sleeve having suitable thermal-expansion and stiffness characteristics to provide the desired consolidation while the temperature of the assembly is increased to a resin curing temperature. One suitable material comprises silicone rubber, which has a volumetric thermal-expansion coefficient of about 7×10⁻⁴ K⁻¹ and a Young's modulus of about 4×10⁶ N/m². Suitable materials may include those that have a volumetric thermal-expansion coefficient between 10⁻⁴ and 10⁻² K⁻¹ and a Young's modulus between 10⁵ and 10⁸ N/m². Other examples of materials that may be used for the sleeve include various rubbers or heat-activated shrink polymers, which may be provided in the form of tape, tubing, or the like. Alternative structures such as pressurized bladders or clamping molds may be used in other cases to provide the compressive force. Some other source of external pressure such as may be provided with a pressurized containment system may also be used to provide the compressive force in other embodiments.

The resin is cured thermally to the green-state at block 316 by raising the temperature of the preceramic resin to a curing temperature, with the compressive force active to provide consolidation pressure to accommodate the natural expansion of the resin during the temperature change. A variety of different techniques may be used to cure the resin, including the use of direct heat by placing the assembly in an over or furnace or through the use of locally mounted heaters. In other embodiments, the resin is heated resistively by passing a current through the conductor. It will be appreciated that the availability of the various types of curing and consolidation techniques permit installation to be accomplished in a variety of different venues, including in the field, in a remote location, in a manufacturing facility, or the like. Assembly in the field or in a remote location may advantageously avoid the use of a large, permanently mounted oven or furnace.

After the green-state insulation has been formed by curing the resin, the compressive force may be removed as indicated at block 320. Depending on how the compressive force was applied, such removal may comprise removing a sleeve from the assembly, removing the assembly from a pressurized containment system, or the like. If the method included the use of a resin containment and release film, that material may also be removed at block 320.

The flow diagram of FIG. 3B summarizes methods for applying insulation that accommodates joints in the conductor. Partially insulated electrical conductors are provided at block 324. The insulation on these conductors may have been formed using a method like that described in connection with FIG. 3A or may have been formed with other techniques. The exposed portions of the conductors are generally at one or both ends of the conductors when the conductors are provided with a generally linear shape, but may be in other positions, particular with conductor structures having different shapes.

The uninsulated portions of different conductors are connected at block 328 to form a joint. The joint connection may be made by any suitable technique known to those of skill in the art, including through the use of welding, the use of mechanical links, the use of threaded joints, and the like. Insulation of the joint subsequently begins by coating the joint with preceramic resin at block 332. Generally, the preceramic resin coats the joint structure itself as well as other uninsulated portions of the conductors proximate the joint. Application of a compressive force at block 336 to consolidate the resin during temperature changes to cure the resin thermally at block 340 produce green-state ceramic that insulates the joint. The application of compressive force may be performed using any of the methods described in connection with FIG. 3A, including the placing of a constrained-expansion sleeve around the assembly, placing the assembly in a pressurized containment system, or the like. Similarly, any of the methods described in connection with FIG. 3A may be used to cure the resin thermally, including the use of ovens or furnaces, the use of locally mounted heaters, or the use of resistive heating that results from passing an electrical current through the joined conductors. After curing, the compressive force is removed at block 344.

These methods allow joints to be made and locally electrically insulated between partially insulated conductors in the field or in remote locations, thus enabling arbitrarily long lengths of continuous insulated conductor to be fabricated in the field. In some applications, the length of conductor that may be provided to the field is limited by the stiffness of the conductor and/or the brittleness of the insulation material, which prevent the material from being coiled to a sufficiently small diameter for practical transport to the point of use or installation. This restriction may be accommodated through use of the joint-insulating technique by enabling shorter, transportable lengths of conductor to be provided to the field, where they are joined and insulated to form whatever length is desired for a specific use. Since one factor in the ability to coil the conductor is its thickness, methods of the invention enable field use of conductors having larger thickness, ranging from fractions of an inch to several inches in diameter or greater. These methods also enable certain other specific applications in various embodiments. For instance, other types of insulated conductor that are not otherwise easily joined together may be joined, such as by using the polymer-based insulation to join sections of hermetically sealed mineral insulated cable. In other applications, in-field repair of conductor structures that have been damaged, such as during transportation, handling, or installation procedures. Generally, the methods enable complete fabrication of structures in the field provided that uncured resin can be provided to the field location.

4. In Situ Deployment of Heater Cables

Methods of oil recovery are aided in embodiments of the invention by deploying heater cables into an oil recovery environment with the preceramic resin in a green-state. After deployment, the resin is heated to convert it to form the ceramic insulator, enabling the deployed cables thereafter to be used for thermal oil-recovery processes. The insulation material provides electrical insulating capabilities while in the green-state, during the process of conversion to a ceramic, as well as after it is converted to a ceramic. This enables the heater to aid in the oil-recovery process immediately after installation, as well as prior to and during the conversion process of the preceramic polymer to a ceramic.

An overview of such embodiments is provided with the flow diagram of FIG. 4A. At block 404, the method begins by coating an electrically conductive rod with a preceramic resin, using any of the methods described in connection with FIG. 3A. As indicated at block 408, the resin is cured into a green state, usually through the application of heat at a temperature between 15 and 250° C. In some embodiments, green-staging of the resin is performed at a temperature between 125 and 200° C., being performed at approximately 150° C. in a specific embodiment. In some embodiments, the heater cable is produced by sheathing the rod at block 412. This may be performed by welding the sheath to the insulated rod. In the resulting state, the heater cable may then be deployed into an oil-recovery environment at block 416. Usually such deployment occurs through a well bore or drilled penetration into the oil reservoir or oil shale deposit, or on the surface or near the surface for oil sands applications, although other types of deployment may also be performed depending on the specific configuration of the oil-recovery site.

The green-state resin is pyrolyzed into a ceramic in situ after its deployment in the oil-recovery environment, as indicated at block 420. Such pyrolysis is performed by applying an electric current to the electrical conductor and thereby raising the temperature of the heater cable. Pyrolysis is typically performed at temperatures between 400 and 1500° C., and may be performed at between 750 and 1000° C. in some embodiments. In some instances, the pyrolysis may be performed by application of a ramp-and-soak profile like the one shown for illustrative purposes in FIG. 4B. With such a ramp-and-soak profile, the temperature is increased substantially monotonically for a first period of time and then held at a substantially constant temperature for a second period of time. The profile shown in FIG. 4B includes two stages of ramping and soaking, with the ramping being performed substantially linearly in time. The first stage applies heat at a temperature of about 300° C. for about five hours after a five-hour ramp, and the second stage applies heat at a temperature of about 900° C. for about five hours after a ten-hour ramp. In some cases, multiple ramp and soak stages may be used to completely pyrolyze the preceramic polymer and to provide suitable mechanical and electrical properties in the insulation material. Higher temperatures and faster heating rates can be achieved by applying higher voltages to the conductor within the heater cable, thus further electrically stressing the insulation.

Once the resin has been pyrolyzed at block 420 to form the ceramic insulator, the heater cable may be used in thermal oil-recovery processes as indicated at block 424. Pyrolysis of the resin in situ after deployment in an oil-recovery environment advantageously permits the heater cable to be handled with considerably more versatility before deployment. In particular, when the resin is still in a green-state, the heater cable may be wrapped onto a smaller-diameter spool for packaging and storage when compared with the requirements imposed for a heater cable having a ceramic insulator. This results in a smaller package for transport and may permit a longer length of heater cable to be packaged onto a single spool. In addition, the heater cable with green-state resin is more damage tolerant during deployment, particularly during run-in processes to deploy it downhole, significantly reducing the risk of damage to the insulation during deployment. This technique also enables a wider range of material properties of the ceramic insulator to be used. In particular, the focus for selection of ceramic insulation materials may be on the electrical and mechanical properties most suitable for particular operations in an oil-recovery environment. These considerations need not additionally be constrained by the need to provide high strain tolerance and toughness for efficient transport and deployment of the cables downhole. While the imposition of such constraints on heater cables that include the ceramic insulator may be quite limiting, the desired strain tolerance is much more easily achieved with the green-state resin.

5. Applications

As previously noted, there are numerous applications to the in situ pyrolysis described in detail in connection with FIG. 4A. This includes, in particular, thermal processes used for oil recovery. FIGS. 5 and 6 are flow diagrams that illustrate the integration of in situ pyrolysis with specific exemplary oil-recovery processes. In the case of FIG. 5, this is illustrated for a shale oil-recovery process, while FIG. 6 provides a similar illustration for a thermal tertiary oil-recovery process. The processes are generally similar, demonstrating the ability for embodiments of the invention to apply to a variety of different thermal oil-recovery methods.

The shale oil-recovery process of FIG. 5 begins at block 504 with heater cables being produced with green-state preceramic resin, as described in more detail in connection with FIG. 3. Holes are bored into the shale deposit at block 508, permitting the heater cables produced at block 504 to be deployed into the holes at block 512. A flow of electrical current through the central conductor of the heater cable is used at block 516 to pyrolyze the resin in situ and thereby form a ceramic insulator. The heater cable is then ready for use at block 520 as part of the oil-recovery process by maintaining or increasing its temperature to provide heat in the oil-recovery environment that converts kerogen in the shale to oil. Use of the heater cable in such applications is generally expected to be through the application of a DC voltage to the heater cable, but the invention is not limited to such a usage. Once the kerogen has been converted to oil at block 520, the oil may be pumped to the surface at block 524.

The oil-recovery process illustrated in FIG. 6 may be performed on an oil field and may use multiple extraction techniques to recover as much oil as possible. This is noted at blocks 604 and 608, which respectively identify the performance of primary and secondary oil-recovery processes as discussed above. A thermal tertiary oil-recovery process may use heater cables produced at block 612 with green-state preceramic resin. Holes are bored into the oil field at block 616. In some embodiments, these holes may be bored specifically for use with the thermal tertiary oil-recovery process, but in other instances may be bored earlier in the oil-recovery effort as part of the primary or secondary oil-recovery processes. Irrespective of precisely at which point in the recovery effort the holes are bored, they may be used at block 620 for deployment of the heater cables. In situ pyrolysis of the resin of the heater blocks at block 624 produces a ceramic insulator, thereby creating a heater cable having the desired characteristics for use at block 628. This use may be affected by applying a voltage to the heater cable to generate heat that increases the temperature of oil in the oil field. Use of the heater cable in these applications is generally expected to be through the application of an AC voltage, but the invention is not limited in such a respect. The increase in temperature imparted to the oil in the oil field lowers its viscosity, making it more amenable to pumping to the surface at block 632.

The oil recovered with the embodiments of either FIG. 5 or FIG. 6, or with other thermal methods that use in situ curing of preceramic resin, may subsequently be used for any suitable applications. The in situ processing of the high-temperature insulation described herein can be used for numerous other applications in addition to use in oil recovery. Merely by way of example, this insulation can accordingly be used on heaters, sensors, and other devices that operate at elevated temperature. Installation of the device, with the insulation in the green-state, enables the device or cable to withstand high levels of strain, in bending, tension, or compression, up to and in excess of 2%. This in turn enables compact packaging of long lengths of cable for transport or other uses, or installation of the device through a tortuous path, or reconfiguring the shape of the cable by bending the cable or device into complex or curved shapes within or around a component to be heated. Pyrolysis of the green-state insulation into a ceramic material can be affected by applying a voltage to the conductor contained within the insulation, or by another mechanism of increasing the temperature to an appropriate level to pyrolyze the preceramic insulation. This pyrolysis can be affected during initial and normal operation of the component to be heated or through a special thermal cycle designed to pyrolyze the green-state insulation. Furthermore, the green-state material provides suitable insulation properties to enable the normal operation of the devices while the insulation is in the green-state, while the insulation is undergoing the pyrolysis process, as well as when it is converted into a ceramic. Applications for this insulation material may include, but are not limited to, heaters for industrial ovens and furnaces, pipelines, sub-sea pipelines, heat-treating equipment, vacuum chambers, and many more.

An illustration of field applications that make use of the joint-insulating methods described in connection with FIG. 3B are provided with the flow diagram of FIG. 7 and the corresponding schematic diagrams of FIGS. 8A-8D. The schematic diagrams of FIGS. 8A-8D illustrate configurations during different deployment stages of a heater cable corresponding to different stages in the method of FIG. 7.

The method begins at block 704 by deploying a partially insulated conductor into an oil-recovery environment such as an oil field, oil sands, shale deposit or the like. Any method may have been used to provide partial insulation of the conductor, including use of the methods described above. Deployment of the partially insulated conductor is illustrated in FIG. 8A, which shows an oil-recovery environment 804 that includes a deployment hole within which the partially insulated conductor 808-1 is deployed. In this illustration, the uninsulated portion 812 of the conductor 808-1 is disposed at an end of the conductor 808-1.

As indicated at block 708 and illustrated in FIG. 8B, the exposed portion 812 of the conductor 808-1 is connected with the exposed portion of another partially insulated conductor 808-2. Such connection may be made by any suitable technique, examples of which include the use of welding, the use of mechanical links, the use of threaded joints, and the like. The resulting conductor connection 816 is coated with preceramic resin 820 at block 712, as illustrated in FIG. 8C. The preceramic resin is cured in the field at block 716 to form green-state insulation around the joint and thereby produce a continuous conductor 824 from the two pieces. This continuous conductor 824 may be completely or partially insulated. Examples of circumstances where the continuous conductor 824 is partially uninsulated include those where still further joints are to be made. For instance, the second conductor 808-2 could be uninsulated at both its ends so that it remains uninsulated at one end even after the connection 816 is insulated.

The curing of the joint may include some of the steps described in connection with FIGS. 3A and 3B above. For example, a compressive force may be applied to consolidate the preceramic resin, particularly as the resin expands as the temperature is changed in curing the resin. This may be preceded by application of a resin containment and release film to the conductor, which may be removed after the thermal curing at block 716. The compressive force may be applied by use of a sleeve, by use of pressurized containment system, use of a clamping mold, or the like. The curing itself may be accomplished by passing an electrical current through the conductor connection 816, by using locally mounted heaters, or the like.

After production of the continuous conductor 824 in this way, the portion that corresponds to the additional conductor 808-2 is deployed into the oil-recovery environment at block 720 and as illustrated in FIG. 8D. This process may be repeated with arbitrarily many additional conductors by progressively returning to block 708 to increase the length of the continuous conductor to the desired length for deployment in the oil field. Once deployment has been completed, the continuous conductor 824 may be used for oil recovery at block 724.

In addition to being used in conjunction with initial deployment in an oil-recovery environment, these methods may also be used for the repair, reinforcement, and/or strengthening of conductors used in oil-recovery environments. The methods may be applied to fiber matrix insulation, mineral insulated insulation, or connectors and conductors of insulation.

Thus, having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. For example, the methods described herein for insulating conductors and making insulated joints can be used for numerous applications in addition to their use in oil recovery. For instance, these techniques may be used on heaters, sensors, and other devices that can be insulated using polymer-based insulation systems. Applications for this type of insulation include heaters for industrial ovens and furnaces, pipelines, sub-sea pipelines, heat-treating equipment, vacuum chambers, and many more. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined in the following claims. 

1. A method of producing an insulated electrical conductor, the method comprising: connecting a first electrically uninsulated portion of a first electrical conductor with a second electrically uninsulated portion of a second electrical conductor; coating a joint between the first and second electrically uninsulated portions with a preceramic resin; and heating the preceramic resin to cure the preceramic resin into a green-state insulator that substantially covers the joint.
 2. The method recited in claim 1 further comprising applying a compressive force to the preceramic resin while curing the preceramic resin into the green-state insulator to consolidate the preceramic resin.
 3. The method recited in claim 2 wherein applying the compressive force comprises disposing a sleeve around the preceramic resin, the sleeve being made of a material having a volumetric thermal-expansion coefficient between about 10⁻⁴ and 10−2 K⁻¹ and a Young's modulus between about 10⁵ and 10⁸ N/m².
 4. The method recited in claim 3 wherein the material comprises silicone rubber.
 5. The method recited in claim 2 wherein applying the compressive force comprises applying pressure to the preceramic resin with a pressurized containment system.
 6. The method recited in claim 2 wherein applying the compressive force to the preceramic resin comprises: applying a resin containment film to the preceramic resin; and disposing a sleeve around the resin containment film, the method further comprising removing the sleeve and the resin containment film.
 7. The method recited in claim 1 wherein each of the first and second electrical conductors comprises an electrically insulated portion.
 8. The method recited in claim 1 wherein each of the first and second electrical conductors comprises a solid electrically conductive rod.
 9. The method recited in claim 1 wherein each of the first and second electrical conductors comprises a stranded electrical conductor.
 10. The method recited in claim 1 wherein curing the preceramic resin into the green-state insulator comprises passing an electrical current through the first and second electrical conductors.
 11. The method recited in claim 1 wherein curing the preceramic resin comprises curing the preceramic resin in a field location with locally mounted heaters.
 12. A method of assisting an oil-recovery process, the method comprising: deploying a first electrical conductor into an oil-recovery environment, the first electrical conductor comprising a first electrically uninsulated portion; connecting the first electrically uninsulated portion with a second electrically uninsulated portion of a second electrical conductor; coating a first joint between the first and second electrically uninsulated portions with a preceramic resin; curing the preceramic resin to convert the preceramic resin into a green-state insulator that substantially covers the first joint to form a continuous conductor; applying a compressive force to the preceramic resin while curing the preceramic resin to consolidate the preceramic resin; and deploying at least a portion of the continuous conductor corresponding to the second electrical conductor into the oil-recovery environment.
 13. The method recited in claim 12 further comprising: coating a portion of the first electrical conductor with the preceramic resin before deploying the first electrical conductor into the oil-recovery environment; and pyrolyzing the preceramic resin of the coated portion to convert the preceramic resin of the coated portion into a ceramic insulator that electrically insulates the portion, wherein pyrolyzing the preceramic resin of the coated portion is performed before connecting the first electrically uninsulated portion with the second electrically uninsulated portion.
 14. The method recited in claim 12 further comprising: connecting a third electrically uninsulated portion of the second electrical conductor with a fourth electrically uninsulated portion of a third electrical conductor; coating a second joint between the third and fourth electrically uninsulated portions with the preceramic resin; curing the preceramic resin coating the second joint to convert the preceramic resin into a green-state insulator that substantially covers the second joint to form the continuous conductor; applying a second compressive force to the preceramic resin coating the second joint while curing the preceramic resin coating the second joint to consolidate the preceramic resin; and deploying a portion of the continuous conductor corresponding to the third electrical conductor into the oil-recovery environment.
 15. The method recited in claim 12 wherein applying the compressive force comprises disposing a sleeve around the preceramic resin, the sleeve being made of a material having a volumetric thermal-expansion coefficient between about 10⁻⁴ and 10⁻² K⁻¹ and a Young's modulus between about 10⁵ and 10⁸ N/m².
 16. The method recited in claim 15 wherein the material comprises silicone rubber.
 17. The method recited in claim 15 wherein applying the compressive force comprises applying pressure to the preceramic resin with a pressurized containment system.
 18. The method recited in claim 15 wherein applying the compressive force to the preceramic resin comprises: applying a resin containment film to the preceramic resin; and disposing a sleeve around the resin containment film, the method further comprising removing the sleeve and the resin containment film.
 19. The method recited in claim 12 wherein pyrolyzing the preceramic resin comprises passing an electrical current through the first and second electrical conductors. 